Up-and-coming U.S. Senate candidate Marco Rubio has become the hottest ticket on Florida's tea-party circuit. The movement of disaffected, disillusioned and generally fed up conservative voters has helped fuel his increasingly competitive campaign against the more moderate Gov. Charlie Crist.

Here's the problem: Rubio, the Republican former leader of the Florida House, could be sidelined as a fringe candidate if he is too closely associated with the loosely organized, quirky tea party crowd. When a recent New York Times headline asked: "The first senator from the tea party?" Rubio spokesman Alex Burgos quipped: "At least they put a question mark."

The impact of tea party voters on the 2010 election is as unpredictable as the political climate in the nation's largest swing state. That uncertainty keeps Rubio straddling two worlds: the traditional Republican establishment and the unconventional grass roots movement.

"The thing that protects candidates from being perceived as extreme and outside the mainstream is whether they are optimists, and Marco is very optimistic about America," said national Republican strategist Alex Castellanos. "What helps Rubio transcend is his passion against what Washington is doing but also the optimism that we can do better."

Rubio has been to at least seven tea party demonstrations in Florida and is slated to attend his eighth rally Saturday in Inverness. But he is skipping the movement's first national convention, headlined by former vice presidential nominee Sarah Palin next month, even though the Nashville event would offer opportunities for publicity and fundraising.

And Rubio's campaign, which typically ballyhoos national media attention, declined to circulate recent praise from New York Times columnist David Brooks, who pegged Rubio as a "bright and polished politician'' who could transform "an amateurish (tea party) movement with mediocre leadership."

Rubio portrays himself as a bridge between the GOP and the tea party.

"The desire to have a Republican Party that is a viable, strong and consistent genuine alternative to what's happening in Washington is the very focus of our campaign," he said at a recent GOP meeting. "The tea party's a part of that, but there's a lot of traditional Republicans that find themselves in that demographic as well."

There may be as many types of tea partiers as there are flavors of tea. One challenge for the campaign is that many activists are registered as independents or as Democrats, making them ineligible to vote in the Republican primary.

The movement is largely a backlash against what it perceives as Washington's big-government, big-spending ways, though people who attend the rallies have other causes, too: curbing illegal immigration, bashing climate change initiatives, and even questioning President Barack Obama's citizenship.

Crist, whose support for Obama's costly economic spending plan has chipped away at his Republican following, has steered clear of the rallies.

In contrast, Rubio's stump speech is like red meat to these crowds, with its rallying cry of God bless America and the free market system.

"I'm here today as a fellow American whose parents were born in a country that lost itself to socialism," the 38-year-old Cuban-American told a cheering audience in West Palm Beach last year. "My parents lost their country to a government. I will not lose mine to a government."

While the rallies have helped Rubio hone his message and build momentum, he, in turn, has helped an amorphous movement find its voice and gain credibility. Rubio is an experienced politician and charismatic speaker who can draw a crowd.

"I invited him about five times," said retiree Edna Mattos, who is organizing Saturday's rally in Inverness. "I e-mailed. I called. I've been a real pest. … He is a favorite with the grass roots. You can feel he is one of us."

Not true, says the Crist campaign, which has been attacking Rubio on the grounds that his message diverges from his record. The campaign released an Internet ad Tuesday that accuses Rubio of changing his positions on immigration, cap-and-trade policy and taxes.

"Whether it's tea party activists or Republican primary voters, they will see that what Marco Rubio says on the stump doesn't match his record," said Crist's campaign manager, Eric Eikenberg.

The Rubio campaign called the Crist ad "false'' and pointed to flip-flops by Crist on the same issues.

Whether Rubio — and the GOP — can channel the tea party energy into money and votes is one of the biggest questions hovering over the 2010 election.

"You've got this energy and anger, with people ready to work for anyone that espouses the principles that we believe in," said Brevard County activist Matt Nye, who is compiling a database of tea partiers. "There is a tremendous surge of activity and the Republican Party is recognizing that."

Times political editor Adam C. Smith contributed to this report.

Tea party gathering

U.S. Senate candidate Marco Rubio will attend a rally at 1 p.m. Saturday at the Old Courthouse in Inverness.

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